Colon: impaction in Horses (Equis) | Vetlexicon
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Colon: impaction

ISSN 2398-2977


  • Colonic impaction (or accumulation of ingesta in the colon that causes obstruction) is a cause of colic.
  • Pelvic flexure impactions are the most common cause of colonic impactions.
  • Cause: poorly digested food, ingestion of sand, changes in management and/or feeding, abnormalities of dentition, stress and travel, and change in water intake and dehydration are some of the factors attributed to the development of impactions.
  • Signs: chronic low-grade colic, that is generally present over several days. There may be secondary dehydration, but cardiovascular compromise is usually minimal.
  • Diagnosis: rectal examination is usually diagnostic for pelvic flexure impactions but may not be diagnostic for right dorsal colon impactions.
  • Treatment: medical treatment with fluids, analgesics and laxatives is generally effective, although surgery is indicated in a minority of cases.
  • Prognosis: usually good in medical cases.

Presenting signs

  • Low grade, chronic and unremitting abdominal pain Abdomen: pain - adult.
  • Gradual onset and slow progression of disease.
  • Signs usually involve depression and anorexia, rather than side kicking, rolling, and sweating.
  • Cardiovascular compromise is rarely a feature.

Acute presentation

  • Signs of mild to moderate abdominal pain.

Geographic incidence

Age predisposition

Gender predisposition

  • May occur without sex predisposition.

Public health considerations

  • Small colon impactions have an increased association with Salmonella Salmonella spp shedding and should be treated as such with isolation from other horses and personal protective equipment.

Cost considerations

  • Usually responds to medical treatment alone, but may take several days during which continued monitoring is usually necessary.

Special risks

  • Uncommonly, cases may need surgical evacuation of the colonic contents, in which case, anesthetic considerations should be made.
  • In addition, in cases that do undergo surgery, careful attention must be made by the surgeon to gentle handling of the tissue, as colonic rupture is a possibility.



  • Most colonic impactions occur in the large colon, particularly at the pelvic flexure and right dorsal colon. Impactions arise most commonly at sites where there is transition of intestinal movement, at sphincters between different segments of intestine, or at regions of intestinal narrowing. The causes in many cases remain unknown but possibilities include:
    • Poor teeth and thus poor mastication of food.
    • Stress associated with transport, etc.
    • Inadequate or inappropriate food (coarse roughage).
    • Parasitism.
    • Systemic dehydration.
    • Eating of bedding or other inappropriate material that is poorly digested.
    • Gastric ulceration, intestinal adhesions.
    • Lack of sufficient water.
    • Sudden change in management, especially exercise or diet.
  • Cases are particularly common in horses that are suddenly put onto box rest, in many cases these are fit animals who are on high rations. Change in feed rations and boredom encourage them to eat their bedding.
  • Sub-acute grass sickness Grass sickness.
  • Infrequent feeding.
  • Damage to colonic nervous system due to previous colonic distention affecting colonic motility.
  • Small colon impactions can occur for the same reasons, but many are idiopathic. Interestingly, one survey showed 25% of those horses that went to surgery for correction of a small colon impaction were Salmonella positive.
  • See Rectum: meconium impaction.
  • Acquired narrowing of the colon due to trauma, neoplasia, or previous surgery.

Predisposing factors


  • Recent change in environment or regime.
  • Poor dentition.
  • Inadequate, inappropriate or poor quality feeding.
  • Parasitism.
  • Decreased or lack of sufficient water.
  • Travel and stress.


  • Inadequately digested food matter (or foreign bodies) accumulates in colon. Though properly digested, good quality food matter can also become dehydrated and impacted with decrease water intake and decreased motility.
  • A blockage of the intestinal lumen results.
  • The impacted ingesta becomes progressively harder and drier with time, and thus more and more solid.
  • Peristaltic waves may become weaker due to the presence of a blockage.
  • Dehydration may occur due to decreased eating and drinking.
  • Poorly understood.
  • Impactions tend to occur at sites where there is physical change in: Either The course of the gut lumen, so a partial 'kink' is present, encouraging ingesta to build up. Or Size of gut lumen, ie pelvic flexure and transverse colon. Or due to a pre-existing luminal obstruction such as enterolith or tumor.
  • Abnormal gut motility may be as important in the development of this disease as the character of ingesta.
  • Poor GI motility can occur on box rest, since exercise promotes peristaltic activity. Other factors such as lack of fresh grass can be involved.
  • Horses living in a sandy environment may slowly eat and accumulate sand within their colon which gradually creates a narrowing of the lumen and predisposition for obstruction Gastrointestinal: sand colic.
  • Correlation with presence of Salmonella Salmonella spp may also be associated with that organism's effects on gut motility.


  • Usually a chronic timecourse, involving a gradual build-up of the impaction within, and then a gradual worsening of symptoms. If more serious sequela result, the presentation can even appear to be acute.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Blikslager A T (2019) Colic prevention to avoid colic surgery: a surgeon's perspective. J Equine Vet Sci 76, 1-5 PubMed.
  • Kilcoyne I, Dechant J E, Spier S J, Spriet M & Nieto J E (2017) Clinical findings and management of 153 horses with large colon sand accumulations. Vet Surg 46 (6), 860-867 PubMed.
  • Williams S, Horner J, Orton E, Green M et al (2015) Water intake, faecal output and intestinal motility in horses moved from pasture to a stabled management regime with controlled exercise. Equine Vet J 47 (1), 96-100 PubMed.
  • Jennings K, Curtis L, Burford J & Freeman S (2014) Prospective survey of veterinary practitioners' primary assessment of equine colic: clinical features, diagnoses, and treatment of 120 cases of large colon impaction. BMC Vet Res.10 Suppl 1 PubMed.
  • Gunnarsdottir H, Van der Stede Y, De Vlamynck C et al (2014) Hospital-based study of dental pathology and faecal particle size distribution in horses with large colon impaction. Vet J 202 (1), 153-156 PubMed.
  • Hart K A, Linnenkohl W, Mayer J R et al (2013) Medical management of sand enteropathy in 62 horses. Equine Vet J 45 (4), 465-469 PubMed.
  • McGovern K & Bladon B (2011) Medical management of large colon obstruction in the horse. In Pract 33 (5), 205-208 VetMedResource
  • Monreal L et al (2010) Enteral fluid therapy in 108 horses with large colon impactions and dorsal displacements. Vet Rec 166 (9), 259-263 PubMed.
  • Riley E, Martingale A et al (2007) Small colon lipomatosis resulting in refractory small colon impaction in a Tennessee Walking Horse. Equine Vet Educ 19 (9), 478-481 VetMedResource.
  • Schumacher J & Mair T S (2002) Small colon obstructions in the mature horse. Equine Vet Educ 14 (1), 19-28 VetMedResource.
  • Debarainer R M & White N A II (1995) Large colon impaction in hoses - 147 cases (1985-1991). JAVMA 206 (5), 679-685 PubMed.
  • Proudman C J (1992) A two year, prospective study of equine colic in general practice. Equine Vet J 24 (2), 90-93 PubMed.

Other sources of information

  • Rose R J & Hodgson D R (1993) Manual of Equine Practice. Saunders. ISBN 0 7216 3739 6.